1. Technical Field
The present invention relates to a vehicle controller provided with a power storage device.
2. Related Art
As a driving assistance system, a constant speed traveling system that maintains a prescribed vehicle speed or a cruise control system has been developed. Furthermore, there has been developed a cruise control system that uses a millimeter wave radar, infrared laser, stereo camera unit, monocular camera or the like to collect information on a preceding vehicle so as to cause the vehicle with the system to follow the preceding vehicle. Such cruise control systems are used in electric vehicles and hybrid vehicles that use one or more electric motors for propulsion.
It is desirable that the hybrid vehicles increase their motor traveling ranges within which they are capable of running on only an electric motor in order to actively switch off an engine for enhanced fuel economy. For this purpose, a hybrid vehicle has been proposed that, when approaching a preceding vehicle, predicts that the driver does not make a request for acceleration, and lifts restrictions on electric motor torque to increase the motor traveling range (see Japanese Unexamined Patent Application Publication (JP-A) No. 2012-240566). In other words, under a driving condition in which no driver request for acceleration is predicted, the torque margin of the electric motor reserved for acceleration is reduced, while the electric motor output torque is raised, thereby expanding the motor traveling range.
There has also been developed a driving assistance system that uses a millimeter wave radar, infrared laser, stereo camera unit, monocular camera or the like to perform forward monitoring and, if a vehicle crash is predicted, automatically brakes the vehicle. Hybrid vehicles and electric vehicles are provided with a regenerative braking system that enables regeneration of the electric motor. However, the braking force provided by the regenerative braking system is limited by the battery's capacity to store electricity, making it impossible to increase the braking force depending on the state of charge or temperature of the battery. In addition, regenerative electric power provided in conjunction with regenerative braking is supplied to the battery, which may pose a risk of the battery overcharging depending on the state of charge or temperature of the battery. To solve this concern, a hybrid vehicle has been proposed that, if there is a risk of the battery overcharging, causes the regenerative electric power provided in conjunction with regenerative braking to be consumed by other electric motors to avoid battery overcharging (JP-A No. 2010-111182).
Even if electric motor torque margin is reduced as described in JP-A No. 2012-240566, the performance of a battery or capacitor as a power storage device cannot be optimized, which may result in restrictions on a motor traveling range. In other words, since the charge/discharge range available to the power storage device may be narrowed by temperature conditions and state of charge, just increasing electric motor output torque may limit the motor traveling range. In addition, when an attempt is made to set the charge/discharge range for the power storage device, the charge/discharge range must be narrowed in consideration of an overshoot or undershoot associated with charge/discharge in order to prevent the power storage device from being overcharged or over-discharged. As a result, the performance of the power storage device cannot be optimized, making it difficult to expand the motor traveling range. In hybrid vehicles as well as electric vehicles, optimization of the power storage device's performance is essential to reduce electric vehicle power consumption.
With the automatic brake control for the aforementioned driving assistance system, it is important to increase braking force quickly and strongly if there is determined to be a risk of a vehicle crash. In other words, it is important to increase the braking force of the regenerative brake under automatic brake control. However, as described above, since the braking force of the regenerative brake is limited by the capacity of the battery to store electricity, the performance of the power storage device cannot be optimized depending on battery state of charge or temperature, making it difficult to increase braking force. In addition, from the viewpoint of the automatic brake control, it is necessary to optimize the performance of the power storage device.